Bug 2298206 (CVE-2022-48862)

Summary: CVE-2022-48862 kernel: vhost: fix hung thread due to erroneous iotlb entries
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: kernel 5.15.29, kernel 5.16.15, kernel 5.17 Doc Type: If docs needed, set a value
Doc Text:
A vulnerability was found in the Linux kernel's vhost driver in the vhost_iotlb_add_range_ctx function, which can lead to a hung thread due to erroneous IOTLB entries. This occurs when a zero-sized range is incorrectly processed, resulting in an infinite loop during packet transmission when accessing the IOTLB leads to DoS.
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Description OSIDB Bzimport 2024-07-16 13:34:11 UTC 
In the Linux kernel, the following vulnerability has been resolved:

vhost: fix hung thread due to erroneous iotlb entries

In vhost_iotlb_add_range_ctx(), range size can overflow to 0 when
start is 0 and last is ULONG_MAX. One instance where it can happen
is when userspace sends an IOTLB message with iova=size=uaddr=0
(vhost_process_iotlb_msg). So, an entry with size = 0, start = 0,
last = ULONG_MAX ends up in the iotlb. Next time a packet is sent,
iotlb_access_ok() loops indefinitely due to that erroneous entry.

	Call Trace:
	 <TASK>
	 iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
	 vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
	 vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
	 vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
	 kthread+0x2e9/0x3a0 kernel/kthread.c:377
	 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
	 </TASK>

Reported by syzbot at:
	https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87

To fix this, do two things:

1. Return -EINVAL in vhost_chr_write_iter() when userspace asks to map
   a range with size 0.
2. Fix vhost_iotlb_add_range_ctx() to handle the range [0, ULONG_MAX]
   by splitting it into two entries.